Coaxial electrograms demonstrate directional independence and enhanced far-field rejection, as well as accurate activation determination in fibrotic substrates

Background Accurately identifying local activation times in extracellular electrograms is highly valuable for successful catheter ablation of cardiac arrhythmias. We previously demonstrated that coaxial electrograms, using only three equally distributed local references, are superior to bipolar electrograms for determining local activation in the healthy heart. Purpose To validate directional independence and far-field rejection capabilities of coaxial compared to bipolar electrograms across multiple wavefront angles and substrates. Method We used a 5x5 cm 2D tissue slab-based cardiac computer model. Local activation was determined in unipolar and coaxial electrograms as dV/dt_(min), and in bipolar electrograms as V_(max) of absolute potential. As golden standard we used the maximum dV/dt of the upstroke of the local action potential. Next, we fabricated multi-electrode sensor grids to compare unipolar and bipolar electrograms against coaxial electrograms based on three or four equally distributed local references. Epicardial electrograms were recorded from three Langendorff-perfused pig hearts using grids with 3, 6, and 9 mm electrode spacing, 0.5 and 1 mm² and electrode sizes. Results In silico, activation in the unipolar and cross- and triangular coaxial electrograms occurred within 1 ms of the golden standard in 100% of the electrode locations. In bipolar electrograms that were longitudinal or perpendicular to the wavefront, this was only the case in respectively 7% and 30% of these locations. The accuracy of the unipolar and coaxial did not depend on wavefront direction. These results were consistent with ex vivo recordings from isolated hearts, which showed no significant difference in local activation between unipolar and coaxial electrograms regardless of wavefront direction. Far-field reduction was assesed ex vivo by applying a subthreshold pulse. The amplitude of this pulse was 2–7 times lower in the coaxial electrograms than in the bipolar electrograms, depending on the inter-electrode spacing and electrode size. Finally, in silico results showed superior accuracy of coaxial electrograms in determining local activation in the presence of fibrosis. Both unipolar and coaxial electrograms estimated local activation within 1 ms from the golden standard in ±80% of the locations whereas this was only the case in 8-20% of the bipolar electrograms. Conclusion Coaxial electrograms, using three or four local references, are both superior to bipolar electrograms in terms of reducing far-field effects and could enable more accurate local activation determination in the presence of fibrosis.